Apparatus and method for straightening tubes

ABSTRACT

Apparatus for straightening a tube includes a measuring device which is located within the bore of the tube, and a tube straightening mechanism, the tube being moved relative to both the measuring device and the straightening mechanism. The measuring device generates a control signal representing lack of straightness in the tube and this is applied to the straightening mechanism and determines the straightening force applied to the tube. A second measuring device may be located within that portion of the tube on which the straightening mechanism acts, to generate a feedback signal.

United States Patent [191 Ritchie [4 1 Feb. 18, 1975 1 APPARATUS ANDMETHOD FOR STRAIGHTENING TUBES [75] Inventor: William Kerr Ritchie,Woodbridge,

England [73] Assignee: The Post Office, London, England [22] Filed: May14, 1973 [21] Appl. No.: 359,897

[30] Foreign Application Priority Data May 18, 1972 Great Britain23372/72 [52] US. Cl. 72/9, 72/12 [51] Int. Cl B2ld 3/10 [58] Field ofSearch ..72/9,10,ll,l2,17,18, 72/31, 208, 209, 367, 370, 393; 33/302,303, 312

[56] References Cited UNITED STATES PATENTS 1,783,797 12/1930 Klein72/420 3,030,901 4/1962 McConnell 72/31 3,316,743 5/1967 Ovshinsky 72/103,335,587 8/1967 Blachut 72/10 3,460,028 8/1969 Beaver ct a1...3,496,644 2/1970 Short 3,566,640 3/1971 Harringt0n..... 3,602,031 8/1971Graff 72/393 Primary Examiner-C. W. Lanham Assistant ExaminerM. J.Keenan Attorney, Agent, or Firm-Hall & Houghton [57] ABSTRACT Apparatusfor straightening a tube includes a measuring device which is locatedwithin the bore of the tube, and a tube straightening mechanism, thetube being moved relative to both the measuring device and thestraightening mechanism. The measuring device generates a control signalrepresenting lack of straightness in the tube and this is applied to thestraightening mechanism and determines the straightening force appliedto the tube. A second measuring device may be located within thatportion of the tube on which the straightening mechanism acts, togenerate a feedback signal.

16 Claims, 1 Drawing Figure APPARATUS AND METHOD FOR STRAIGHTENING TUBESThis invention relates to the straightening of tubes,

and is particularly applicable to the straightening of 5 tubes for useas waveguides.

A high order of straightness is required in tubes for use as waveguidesand it is often necessary to straighten imperfect tubes. Traditionalmethods of tube straightening aim to straighten the outside of the tube:one method relies on visual observation of curvature in the tube and theapplication of a correcting force at an appropriate number of pointsalong the tube and in another method the tube is passed through a seriesof angled rollers which rotate the tube and apply to it a series ofbending movements. In the case of a waveguide tube, however, it is theatraightness of the bore of the tube that is of importance so that thetraditional methods are only applicable to tubes in which the wallthickness is uniform. Moreover the accuracy of traditional methods ispoor.

The present invention provides apparatus for straightening a tube,including a measuring device locatable within the bore of the tube andoperable to generate a control signal representativeof the deviationfrom straightness in the surrounding portion of the tube; a tubestraightening mechanism connected to receive the control signal andoperable to apply, to a portion of the tube, a straightening forcedependent on the value of the control signal derived from that portion;and a mechanism operable to effect relative movement between the tubeand both the measuring device and straightening mechanism.

In a preferred embodiment of the invention, the mechanism for effectingrelative movement is operable to effect continuous relative movementbetween the tube and both the measuring device and straighteningmechanism. In this embodiment, the measuring device is operable togenerate a continuous control signal.

The apparatus may include a second measuring device which is locatablewithin the bore of the tube in that portion of the tube on which thestraightening mechanism is operable, the second measuring device beingoperable to generate a feedback signal represen tative of the deviationfrom straightness in the surrounding portion of the tube, and thestraightening mechanism also being connected to receive the feedbacksignal and to apply the straightening force in dependence on therelative values of the control and feedback signals. The straighteningmechanism may, for example, include a differential amplifier connectedto receive both the control signal and the feedback signal and operableto produce an error signal in dependence on the relative values of thosesignals. The differential amplifier may be connected to receive thecontrol signal through a control amplifier the gain of which isadjustable and which has an adjustable input/output characteristic.

In an embodiment of the invention, the straightening mechanism is spacedapart from the measuring device in the direction of the relativemovement of the tube and is connected to receive the control signal fromthe measuring device through a delay equal to the time required for aportion of the tube to reach the straightening mechanism from themeasuring device when the apparatus is in use. The delay is preferablyadjustable in response to variations in the speed of the relativemovement.

The apparatus may include a third measuring device which is locatablewithin the bore of the tube in a portion of the tube on which, when theapparatus is in use, the straightening mechanism has operated, the thirdmeasuring device being operable to generate a signal representative ofthe deviation from straightness in the surrounding portion of the tube.

The apparatus may include recording means connected to receive andrecord the signals generated by the first, second and third measuringdevices.

The straightening mechanism may include an adjustable die engageablewith the tube to apply the straightening force thereto.

The present invention also provides a method of straightening a tube,including the steps of locating within the bore of the tube a measuringdevice operable to generate a control signal representative of thedeviation from straightness in the surrounding portion of the tube;effecting relative movement between the tube and the measuring device sothat the measuring device generates a control signal representative ofthe deviation from straightness along the length of the tube, andeffecting relative movement between the tube and a tube straighteningmechanism and applying the control signal to the straightening mechanismto operate the latter to apply a straightening force to the tube. Therelative movement between the tube and the straightening mechanism maybe effected simultaneously with the relative movement between the tubeand the measuring device, in which case the control signal generated bythe measuring device is applied to the straightening mechanism after adelay equal to the time required for a portion of the tube to reach thestraightening mechanism from the measuring device. Alternatively, therelative movement between the tube and the straightening mechanism maybe effected after the relative movement between the tube and themeasuring device, in which case the control signal generated by themeasuring device is recorded and subsequently applied to thestraightening mechanism.

In a preferred method in accordance with the invention, the relativemovement between the tube and the measuring device is continuous and themeasuring device generates a continuous control signal. In thispreferred method, the relative movement between the tube and thestraightening mechanism is continuous, and the straightening mechanismapplies a continuous straightening force to the tube. Alternatively,however, the straightening mechanism may be operated to apply astraightening force to the tube at points spaced apart along the tube.

The method may also include the step of generating a feedback signalrepresentative of the deviation from straightness in the portion of thetube to which the straightening force is being applied and applying thatfeedback signal to the straightening mechanism.

The method may also include the step of measuring the deviation fromstraightness in a portion of the tube to which the straightening forcehas been applied.

By way of example, apparatus and methods in accordance with theinvention will be described with reference to the accompanying drawingwhich is a diagram of apparatus for straightening waveguide tubes.

The drawing illustrates the apparatus in use, that is with a waveguidetube 1 in the process of being straightened. The apparatus includesthree straightness measuring heads 3, 5, 7 located within the bore ofthe tube 1, and a straightening mechanism which is indicated generallyat 9 and through which the tube extends. The measuring heads 3, 5, 7 andthe straightening mechanism 9 are all fixed, while the tube 1 is eitherpushed or pulled lengthwise through the apparatus at an appropriatespeed in the direction indicated by the arrow 11. The mechanism formoving the tube can be of any suitable type: it may, for example,include a pair of resiliently-mounted rollers 35 which have a highcoefficient of friction with the tube and are positioned close to thestraightening mechanism 9, on the approach side of the latter, to engageand push the tube through the straightening mechanism.

The straightening mechanism 9 comprises two fixed dies 13 between whichis located an adjustable die 15 movable in one plane by hydraulic rams17. The measuring heads 3, 5, 7 are spaced apart lengthwise of the tube1 with the head being positioned within the adjustable die and the heads3 and 7 being positioned respectively before and after the straighteningmechanism 9 (relative to the direction of movement of the tube 1).

Each of the heads 3, 5, 7 measures the deviation from straightness (ifany) in the bore of the surrounding portion of the tube 1, and may be ofany suitable type. The measuring heads shown in the drawing are all of aknown type and will, therefore, be described only briefly. Each head hasa central portion 19 which is shown only diagramatically in the drawingbut which comprises a pair of parallel beams (typically about 20 cms.long) from each of which a set of three feet 21, 22 and 23 extends. Thefeet in each set are spaced apart lengthwise of the tube with the outerfeet 21 and 23, which are located near the ends of the beam, beingfixed. The two sets of feet are diametrically-opposed and the beams arespring-loaded apart so that the fixed feet 21 and 23 engage the innersurface of the tube 1. Each of the centre feet 22 is mounted on the coreof a transformer, forming a displacement transducer, and is movable withthe core relative to the respective beam. Each core is spring-loaded sothat the centre feet 22 also engage the inner surface of the tube 1 andthe transducers are arranged to give a linear relationship between coremovement and the transducer output signal. Any lack of straightness inthe bore of the tube 1 will be indicated by an electrical output signalfrom the transducers, caused by movement of the centre feet 22: outputsignals resulting from variations in the diameter of the bore, ratherthan lack of straightness, can be eliminated by subtracting the outputsof the diametrically-opposed transducers.

The measuring heads 3, 5 and 7 are mounted within the tube 1 so thatthey will not move longitudinally or rotate while the tube is beingmoved through the apparatus, but so that they are capable of aligningwith the bore of the tube. This may be achieved by using an assembly ofrods and universal joints to connect the measuring heads 3, 5 and 7through the bore of the tube 1, to an external mounting.

The output of the first measuring head 3 is connected, through avariable delay 25, to a variable gain amplifier 27 which has a variableinput/output characteristic. The output of the amplifier 27 is appliedto a differential amplifier 29 which also has an input from the secondmeasuring head 5. The output of the differential amplifier 29 is appliedto a hydraulic system 31 which controls operation of the rams 17 in thestraightening mechanism 9. The outputs of all three measuring heads 3,5, 7 are applied to respective pens (indicated by crosses 3', 5, 7') ofa pen-and-paper recorder 33.

The tube 1, as mentioned above, is moved continuously through theapparatus at an appropriate speed and the variable delay 25 is adjustedto equal the time taken for a cross-sectional plane of the tube 1 tomove from the centre feet 22 of the first measuring head 3 to those ofthe second head 5. The variable delay 25 may, for example, be introducedby a magnetic drum or tape with read-on and read-off heads and rotatingor moving, as the case may be, at a speed which is related to thetransit speed of the tube 1 so that variations in the transit speed areunimportant. The first measuring head 3 produces a continuous outputsignal which varies with the curvature in the bore of the tube 1 alongthe length of the tube but, due to the delay 25, the input signal to thevariable gain amplifier 27 represents, at any moment of time, thecurvature in that part of the tube which, at that time, is within thesecond measuring head 5.

The measuring head 5 also produces an output signal proportional to thecurvature in the tube 1 and this is subtracted, in the differentialamplifier 29, from the signal produced by the measuring head 3 for thesame portion of the tube to produce an error signal which is applied tothe hydraulic system to operate the rams 17 and thereby move the die 15which, in association, with 'the fixed dies 13 impresses a correctioncurvature on the tube 1. It will be appreciated from this that themeasuring head 5 actually measures the correction curvature impressed bythe rams l7 and provides a feedback signal to the hydraulic system: withsufficient gain in the feedback loop, the impressed correction curvaturecan be controlled very accurately by the output signal of the firstmeasuring head 3 and can be adjusted very precisely by-altering the gainof the variable gain amplifier 27. The variable input/outputcharacteristic of the amplifier can be used to compensate for thenon-linear nature of the impressed curvature/change-incurvature"characteristic of the tube 1. The term change-in-curvature means thechange actually brought about by the correction process, which can bemeasured from the outputs of the first and third measuring heads 3 and7, since the third head 7 produces an output signal proportional to thecurvature of the tube 1 after passage through the straighteningmechanism 9. Ideally, of course, the curvature after passage through thestraightening mechanism should be zero. It will be appreciated that thecurvatures to be measured by the first and third heads 3, 7 will be muchless than those to be measured by the second head 5 since the lattermeasures impressed curvatures which, to straighten the tube, mustreverse the existing curvatures. The range of the first and third heads3, 7 need not, therefore, be as great as that of the second head 5.

As mentioned above, the outputs of the measuring heads 3, 5 and 7 areconnected to the pens 3', 5' and 7 respectively of the recorder 33. Thetransit speed of the paper of the recorder is related to the transitspeed of the tube 1 and the spacing between the pens 3', 5 and 5', 7 inthe direction of movement of the paper is similarly related to thespacing between the measuring heads 3, 5 and 5, 7 so that superimposedportions of the three traces produced on the paper relate to the sameportion of the tube 1. By observing the traces, an indication can beobtained of the necessary adjustment to the gain and input/outputcharacteristic of the amplifier 27 to obtain the best results from theapparatus.

It will be appreciated from the above that the third measuring head 7 isnot an essential component in so far as straightening the tube 1 isconcerned since it merely provides a check on the effectiveness of thestraightening operation: if such a check is not required then the thirdhead 7 can be omitted. Even if a check on the effectiveness of theoperation is required, the third head 7 can still be omitted and thecheck obtained by passing the tube 1 through the apparatus for a secondtime.

If second measuring head 5 were omitted from the apparatus it would thenbe necessary to operate the apparatus in a predictive manner since thefeedback signal utilized in the apparatus shown in the drawing would notbe produced. It would also be necessary to control accurately the gainin the input circuit to the hydraulic system 31, and the accuracy of thestraightening operation would be limited by play and wear in the dies13, and also by variations in the wall thickness of the tube (bearing inmind that, although the first head 3 measures the curvature of the boreof the tube, the die 15 acts on the external surface of the tube).

Alternatively, the results achieved with the apparatus shown in thedrawing (in which three measuring heads 3, 5, 7 are used and the tube 1makes only one passage through the apparatus) could also be achievedwith apparatus using only one measuring head, by passing the tube threetimes through the apparatus. During the first pass of the tube, themeasuring head would be used in the manner of the first head 3 in thedrawing to measure the curvature of the tube and the output of the headwould be recorded. During the second pass of the tube, the measuringhead would be used in the manner of the second head 5 in the drawing tomeasure impressed curvature, and correction curvatures would be appliedto the tube on the basis of error signals derived from the recordedinformation via the feedback loop. During the third pass of the tube,the measuring head would be used in the manner of the third head 7 inthe drawing to check on the effectiveness of the straighteningoperation.

In the apparatus shown in the drawing, the straightening dies 15 act inone plane only although action in two orthogonal planes may be requiredto straighten the tube 1 completely. This can be achieved most easily byrotating the tube 1 through 90 following the first passage through theapparatus; interchanging the electrical connections of the first andthird measuring heads 3 and 7, and then passing the tube back throughthe apparatus in the opposite direction. The feedback loop through thesecond measuring head 5 is not interrupted during the changeover of theelectrical conec- -tions so that an unstable state will not be broughtabout but it is, of course, essential that the outer measuring heads 3and 7 should have equal sensitivities and be separated by the samedistance from the measuring head 5. As an alternative to reversing thetube and interchanging the electrical connections, the tube could bepassed through the apparatus for a second time in the same directonalthough rotated through 90. A further possibility is to apply astraightening action to the tube in two orthogonal planes during asingle pass through the apparatus although difficulties may arise as aresult of the large number of electrical connections that would berequired to the measuring heads within the tube.

In the apparatus shown in the drawing the correction curvature to beimpressed on the tube 1 in a particular cross-sectional plane by the die15 is derived from a measurement made by the head 3 in that plane only.Under some circumstances this may be insufficient to straighten the tubeadequately and it may be necessary, in deriving the correctioncurvature, to take account also of the curvature of the tube on eitherside of that particular cross-sectional plane. This could be done bymeasuring and recording the curvature of the tube over its whole lengthbefore carrying out any part of the straightening operation, and thenusing the recorded information to calculate the correction curvatures tobe applied along the whole length of the tube during a subsequentpassage through the straightening mechanism 9.

Rollers could be used in the straightening mechanism 9 rather than thedies 13 and 15 described above, with the advantage of a possiblereduction in frictional effects as the tube 1 passes through thestraightening mechanism: there is, however, the disadvantage of apossible loss in accuracy in the straightening action of the apparatus.

The continuous action of the straightening mechanism 9 along the lengthof the tube 1 is not essential and can, under appropriate circumstances,be replaced by a straightening action at points spaced apart along thetube. These points must, however, be close enough to each other toensure that any resulting waves in the tube can be ignored. It is alsonot essential that the relative movement between the tube and themeasuring heads 3, 5, 7 and straightening mechanism 9 should becontinuous and, subject to appropriate modifications being made to theapparatus, discontinuous movement of the tube could be employed.

Finally, it should be mentioned that although the apparatus describedabove makes use of measuring heads 3, 5, 7 which generate electricalcontrol signals it could, as an alternative, be modified to make use ofhydraulic control signals.

I claim:

1. Apparatus for straightening a tube, including first and secondmeasuring devices locatable within the bore of the tube and operable togenerate, respectively, a control signal and a feed back signal, each ofsaid signals being representative of the deviation from straight ness inthe surrounding portion of the tube; a tube straightening mechanismconnected to receive the control and feedback signals and operable toapply, to that portion of the tube in which the second measuring deviceis located, a straightening force dependent on the relative values ofthe control and feedback signals derived from that portion; and amechanism operable to effect relative movement between the tube and boththe measuring devices and straightening mechanism.

2. Apparatus as claimed in claim 1, in which the mechanism for effectingrelative movement is operable to effect continuous relative movementbetween the tube and both the measuring device and straighteningmechanism.

3. Apparatus as claimed in claim 2, in which the measuring device isoperable to generate a continuous control signal.

4. Apparatus as claimed in claim 1, in which the straightening mechanismincludes a differential amplifier connected to receive both the controlsignal and feedback signal and operable to produce an error signal independence on the relative values of those signals.

5. Apparatus as claimed in claim 4, including a control amplifierconnected between the first-mentioned measuring device and thedifferential amplifer, the control amplifier having an adjustable gainand an adjustable input/output characteristic.

6. Apparatus as claimed in claim 1, including a third measuring devicewhich is locatable within the bore of the tube in a portion of the tubeon which, when the apparatus is in use, the straightening mechanism hasoperated, the third measuring device being operable to generate a signalrepresentative of the deviation from straightness in the surroundingportion of the tube.

7. Apparatus as claimed in claim 6, including recording means connectedto receive and record the signals generated by the first, second andthird measuring devices.

8. Apparatus as claimed in claim 1, in which the straightening mechanismis spaced apart from the first mentioned measuring device in thedirection of the relative movement of the tube and including delay meansconnected between the straightening mechanism and the measuring device,the delay means providing a delay equal to the time required for aportion of the tube to reach the straightening mechanism from the firstmentioned measuring device when the apparatus is in use.

9. Apparatus as claimed in claim 8, in which the delay is adjustable inresponse to variations in the speed of the relative movement.

10. Apparatus as claimed in claim 1, in which the straighteningmechanism includes an adjustable die engageable with the tube to applythe straightening force thereto.

11. A method of straightening a tube. including the steps of locatingwithin the bore of the tube a measuring device operable to generate acontrol signal representative of the deviation from straightness in thesurrounding portion of the tube; effecting relative movement between thetube and the measuring device so that the measuring device generates acontrol signal representative of the deviation from straightness alongthe length of the tube; effecting relative movement between the tube anda tube straightening mechanism and operating the latter to apply astraightening force to the tube; generating a feedback signalrepresentative of the deviation from straightness in the portion of thetube to which the straightening force is being applied and applying thatfeedback signal and the control signal to the straightening mechanism tooperate said mechanism.

12. A method as claimed in claim 11, in which the relative movementbetween the tube and the straightening mechanism is effectedsimultaneously with the relative movement between the tube and themeasuring device, the control signal generated by the measuring devicebeing applied to the straightening mechanism after a delay equal to thetime required for a portion of the tube to reach the straighteningmechanism from the measuring device.

13. A method as claimed in claim 11, in which the relative movementbetween the tube and the straightening mechanism is affected after therelative movement between the tube and the measuring device, the controlsignal generated by the measuring device being recorded and subsequentlyapplied to the straightening mechanism.

14. A method as claimed in claim 11, in which the relative movementbetween the tube and the measuring device is continuous and themeasuring device generates a continuous control signal.

15. A method as claimed in claim 14, in which the relative movementbetween the tube and straightening mechanism is continuous, and thestraightening mechanism applies a continuous straightening force to thetube.

16. A method as claimed in claim 11, including the step of measuring thedeviation from straightness in a portion of the tube to which thestraightening force has been applied.

1. Apparatus for straightening a tube, including first and secondmeasuring devices locatable within the bore of the tube and operable togenerate, respectively, a control signal and a feed back signal, each ofsaid signals being representative of the deviation from straightness inthe surrounding portion of the tube; a tube straightening mechanismconnected to receive the control and feedback signals and operable toapply, to that portion of the tube in which the second measuring deviceis located, a straightening force dependent on the relative values ofthe control and feedback signals derived from that portion; and amechanism operable to effect relative movement between the tube and boththe measuring devices and straightening mechanism.
 2. Apparatus asclaimed in claim 1, in which the mechanism for effecting relativemovement is operable to effect continuous relative movement between thetube and both the measuring device and straightening mechanism. 3.Apparatus as claimed in claim 2, in which the measuring device isoperable to generate a continuous control signal.
 4. Apparatus asclaimed in claim 1, in which the straightening mechanism includes adifferential amplifier connected to receive both the control signal andfeedback signal and operable to produce an error signal in dependence onthe relative values of those signals.
 5. Apparatus as claimed in claim4, including a control amplifier connected between the first-mentionedmeasuring device and the differential amplifer, the control amplifierhaving an adjustable gain and an adjustable input/output characteristic.6. Apparatus as claimed in claim 1, including a third measuring devicewhich is locatable within the bore of the tube in a portion of the tubeon which, when the apparatus is in use, the straightening mechanism hasoperated, the third measuring device being operable to generate a signalrepresentative of the deviation from straightness in the surroundingportion of the tube.
 7. Apparatus as claimed in claim 6, includingrecording means connected to receive and record the signals generated bythe first, second and third measuring devices.
 8. Apparatus as claimedin claim 1, in which the straightening mechanism is spaced apart fromthe first mentioned measuring device in the direction of the relativemovement of the tube and including delay means connected between thestraightening mechanism and the measuring device, the delay meansproviding a delay equal to the time required for a portion of the tubeto reach the straightening mechanism from the first mentioned measuringdevice when the apparatus is in use.
 9. Apparatus as claimed in claim 8,in which the delay is adjustable in response to variations in the speedof the relative movement.
 10. Apparatus as claimed in claim 1, in whichthe straightening mechanism includes an adjustable die engageable withthe tube to apply the straightening force thereto.
 11. A method ofstraightening a tube, including the steps of locating within the bore ofthe tube a measuring device operable to generate a control signalrepresentative of the deviation from straightness in the surroundingportion of the tube; effecting relative movement between the tube andthe measuring device so that the measuring device generates a controlsignal representative of the deviation from straightness along thelength of the tube; effecting relative movement between the tube and atube straightening mechanism and operating the latter to apply astraightening force to the tube; generating a feedback signalrepresentative of the deviation from straightness in the portion of thetube to which the straightening force is being applied and applying thatfeedback signal and the control signal to the straightening mechanism tooperate said mechanism.
 12. A method as claimed in claim 11, in whichthe relative movement between the tube and the straightening mechanismis effected simultaneously with the relative movement between the tubeand the measuring device, the control signal generated by the measuringdevice being applied to the straightening mechanism after a delay equalto the time required for a portion of the tube to reach thestraightening mechanism from the measuring device.
 13. A method asclaimed in claim 11, in which the relative movement between the tube andthe straightening mechanism is affected after the relative movementbetween the tube and the measuring device, the control signal generatedby the measuring device being recorded and subsequently applied to thestraightening mechanism.
 14. A method as claimed in claim 11, in whichthe relative movement between the tube and the measuring device iscontinuous and the measuring device generates a continuous controlsignal.
 15. A method as claimed in claim 14, in which the relativemovement between the tube and straightening mechanism is continuous, andthe straightening mechanism applies a continuous straightening force tothe tube.
 16. A method as claimed in claim 11, including the step ofmeasuring the deviation from straightness in a portion of the tube towhich the straightening force has been applied.